1. Field of the Invention
The present invention relates to a magnifying observation apparatus in which an optical imaging device that can obtain an optical image with an optical observation device such as an optical microscope is added to an electron microscope such as a Scanning Electron Microscope (SEM).
2. Description of Related Art
For example, a transmission electron microscope and a scanning electron microscope are well known as a charged particle beam apparatus in which a signal obtained by irradiating an observation target specimen with a charged particle beam is detected to obtain an observation image. In the electron microscope, for example, an electron traveling direction is freely deflected and an image formation system as in an optical microscope is designed in an electro-optical manner. Examples of the electron microscope includes a transmission electron microscope that forms an image of electrons transmitted through a specimen or a sample using an electron lens, a reflection electron microscope that forms an image of electrons reflected from a specimen surface, a scanning electron microscope in which the specimen surface is scanned with a focused electron beam to form an image using secondary electrons from each scanning point, and a surface emission type electron microscope (field ion microscope) that forms an image of electrons emitted from the specimen by heating or ion irradiation (for example, see Japanese Unexamined Patent Publication No. 9-97585).
In the Scanning Electron Microscope (SEM), which is one example of the electron microscope, secondary electrons and reflection electrons generated in irradiating the observation target specimen with a thin electron beam (electron probe) are taken out using detectors such as a secondary electron detector and a reflection electron detector and are displayed on a display screen such as a CRT and an LCD, and a surface mode of the specimen is mainly observed. On the other hand, in the Transmission Electron Microscope (TEM), the electron beam is transmitted through the thin-film specimen, the electrons scattered and diffracted by atoms in the specimen at this time are obtained as an electron diffraction pattern or a transmission electron microscope image, and an internal structure of a substance can mainly be observed.
When a solid-state specimen is irradiated with the electron beam, the electrons are transmitted through the solid-state specimen by electron energy. At this time, elastic collision, elastic scattering, and inelastic scattering associated with energy loss are generated by interaction between electrons and atomic nuclei constituting the specimen. In-shell electrons of a specimen element or X-rays are excited by the inelastic scattering, and the secondary electrons are emitted to lose the energy corresponding to the inelastic scattering. An emission amount of secondary electron depends on a collision angle. On the other hand, an emission amount of reflection electrons that are scattered backward by the elastic scattering and emitted again from the specimen is unique to the atomic number. In the SEM, the secondary electrons and the reflection electrons are utilized. In the SEM, the specimen is irradiated with the electrons, and the emitted secondary electrons or reflection electrons are detected to form the observation image. A Scanning Transmission Electron Microscope (STEM) in which the detector receives light transmitted through the specimen is also well known as one type of the scanning electron microscope.
Although the electron microscopes such as the SEM, the TEM, and the STEM are effectively used in the observation at a high magnifying power, the electron microscopes do not well display at a low magnifying power. Generally, the electron microscope can perform the display of tens thousands times to hundreds thousands times or millions times at the maximum magnifying power. On the other hand, the electron microscope can perform the display of several times to tens times at the minimum magnifying power. For example, in the SEM, the observation can generally be performed at the minimum magnifying power of about 5 times to about 50 times. In the observation with the electron microscope, because the display is performed at the high magnifying power from the beginning, an observation visual field becomes extremely narrow range. Therefore, it is difficult to perform visual field search that is work to finally find a site to be observed on the specimen. Preferably, the visual field search is gradually performed from the wide visual field state, namely, the state in which the specimen is displayed at the low magnifying power to the state in which the visual field is narrowed at the high magnifying power.
In order to facilitate the visual field search of such an electron microscope, there is known a method of utilizing an optical microscope in which visible wavelength light or infrared wavelength light is used and an optical observation apparatus (optical imaging device) (for example, see Japanese Unexamined Patent Publication No. 9-97585). In the observation with the optical imaging device, the display can generally be performed at a low magnifying power of the same size or less. After the specimen is observed at the low magnifying power with the optical imaging device to roughly perform the visual field search, observation is performed with the electron microscope. In order to realize this, the electron microscope is used in conjunction with the observation optical system in which the display can be performed at the lower magnifying power. The visual field search is performed based on the display performed at the low magnifying power with the observation optical system of a CMOS camera or the like. Then, the observation is performed at the high magnifying power while the observation optical system is switched to the electron beam imaging device of the SEM or the like.
In the configuration of Japanese Unexamined Patent Publication No. 9-97585, as illustrated in FIG. 27, a specimen stage provided in a chamber is moved between two imaging devices in order to obtain the images of the specimen in the same visual field from the imaging devices of the optical imaging device and the electron beam imaging device. That is, an imaging device side is fixed, and a specimen side is moved or tilted by a stage driving section, thereby moving and changing the visual field of the observation image. For example, after one specimen is focused from immediately above to obtain the image, an angle between the imaging device and the specimen is changed in order to take the image in a tilt posture. At this time, because a focal distance between each imaging device and the specimen varies each time the angle is changed, it is necessary to correct the focal position. When the images of the specimen are obtained at the same tilt angle with respect to the specimen using the two imaging devices, the angle used in one of the imaging devices is stored, the specimen stage is moved to the other imaging device side, and the angle used in one of the imaging devices is reproduced to fix the focal position. Thus, extremely troublesome adjustment work is required to obtain the same image with the two imaging devices.
Additionally, there is a problem in that the position shift is generated for the heavy specimen in the type in which the specimen stage is oscillated to change a viewpoint while the imaging device side is fixed. That is, when the specimen stage is tilted, a component in a direction along the stage tilting surface is generated in a weight of the specimen. When the specimen stage has a stroke function in the XY-direction, the weight of the XY-stroke may be increased or decreased, and a spring provided to prevent backlash of an XY-axis gear may not work. Therefore, even if the specimen is fastened to the specimen stage so as not to slide down when the specimen stage is tilted, unfortunately the heavy specimen falls unless being securely fastened.
In order to solve the above problems, there is proposed an observation apparatus in Japanese Unexamined Patent Publication No. 5-41194. In the observation apparatus, as illustrated in FIG. 28, XY-stages are prepared for the optical imaging device and the electron microscope, which constitute an observation device 10 in order to place a specimen stage 33X, a specimen SAx is placed on the specimen stage 33X, and the specimen stage 33X placed on the XY-stage is translated by a transfer rod, thereby obtaining the observation position. However, in this configuration, the specimen stage 33X is translated after being pulled out from one of the XY-stages, and the specimen stage 33X is returned to the other XY-stage. Therefore, it is necessary to move the specimen stage 33X in a U-shape, which results in a problem in that a moving mechanism of the specimen stage 33X becomes complicated.
Because the coordinate positions on the XY-stages are independent of each other, coordinates of the XY-stages are not completely matched with each other. Even if XY-coordinate positions on the XY-stages are matched with each other, because the focal position between the observation device and the specimen changes when the image of the specimen is obtained in the tilted posture, it is necessary to correct the focal position. When the images of the same specimen are obtained at the same tilt angle with the two observation devices, the angle used in one of the imaging devices is stored, the specimen stage is moved to the other observation device side, and the angle is adjusted to the stored angle to fix the focal position. Such extremely troublesome adjustment work is required to correctly obtain the images having the same visual field and viewpoint.
Japanese Unexamined Patent Publication No. 10-214583 discloses an electron microscope. As illustrated in FIG. 29, the electron microscope includes a linear translation mechanism that directly moves the specimen stage pulled out from a vacuum chamber to the observation position of the optical imaging device. However, in the electron microscope, because basically the specimen stage is physically moved, it is difficult to correctly match the relative coordinate positions between the plurality of observation devices similarly to Japanese Unexamined Patent Publication No. 5-41194. In both the electron microscopes, it is necessary to insert and pull out the specimen stage in and from the vacuum chamber in switching between the observation devices. Unfortunately, a waiting time is generated in switching between the observation devices, because it takes a long time to evacuate the vacuum chamber after the vacuum chamber is opened and closed. When the translation mechanism is incorporated in the vacuum chamber, unfortunately the vacuum chamber is enlarged to require a large-capacity vacuum pump, and a time necessary for the evacuation is lengthened.